Multistage fluid compressor



April 5, 1927.

' A. W. LIMON-l', JR

MULTIslTAGE FLUID COMPRESSOR Filed June 26, 1926 Sheets-Sheet 1 w. w m m lea/z der WZ'zonZ, JC BY A TTORNEYS.

1623,798 Aprll 5, 1927. A. .wi LIMONT' JR,

' *ULTISTAGE FLUID COMPRESSOR 3 Sheets-Shee't 2 Filed June 26, 1926 www v -mwmm A TTORNEYS.

April 5, 1927.

A. W. LIMQNT. JR

MULTISTAGE FLUID COMPRESSOR Filed June 26, '192e 3 Sheets-Sheet 3 INVENTOR. exa/z der WL z'hzoIz/,

A TTORNEYS.

' 20 vide a piston unit construction@including the l Patented Apr. 5,

ALEXANDER 'wnfLmoNn in, ofiianrnenronag Nominal;` comPANY,1foF SoUtrH No1tvvALx,

DELAWARE? nieuwe@ md .Ilil@llas-,sessel @uw www# comonanoNQF- l t th several *figuresA 'ject to provide; ai ompressprm whichk the; Referring'fofhe wihgfsQt-B"furfsetg'" afford a prper distribution* Work in relatii'elyg\x equal prpoljtions'fper' stage, and anequalization o mechanical effort thruo'ttheirotativefccle.

Another object: isto; yp xftn'fide against" leakage of the expensive and dangerous fluid em@ ployed, and to y'pro`vi`de positive 'Ine'anslfor' collecting any lleakage past tl1e pistonsfand return the same to theintakef'port, thus preventing 'any possibility ofwaste "of lthe d. A further objeot'isto provide an -improved assembly by means "of which fthe parts Ina be readily assembled Vand .accurate yjaligne and conveniently disassembled to remove Vthe pistons, and tothis end itis `Iln'opsed Ato Iproj- 'twp' r. Connecting .ca -amel stepfportion f hereinafter Water ticket. t0; which water: -fhushz-Q nfntkeemps 1.4.5* v-Ats Walid; frame end,;- thecylinderiisclosedfby a hollow cylinder-head secured f16`and provided portion 1T yfittediintqthejendpof thel pistons of the .severalfstages`- and secured at i e. prov1ded 1 with one point to the pistonifod Wherebylremoval of the complete pistonafssemblymay be effectedbjy` disconneatingl at' Vthisfpifnt,l and in.

rfi-assembling, the accnraterelation y of the structure will be assured. It i'sfalso an yob'- all piston assembly f providing', cornpact'nesg unusual rigidity, "andfreedoxnjffrom' vibra.

tion

A still furth" proved water "jacketing, means or' theperf With the above' and","otherI objects@y in4 view,

11n-embodiment Q flffth'e inv y.en iSSShQWh in the accompanyingdra wings, and 'f' bodiment will bef hereinafter "e fully fdc# scribed with'` relieenceigtlier 10,1

40 ventionjwill'-1be finally 1 Fig. 1 is a topplanfvievvfoff'ajfour ta compressor according tq'tliepr ent' ment of the invention Figa 2 is a, side., elevation "thereo Fig. 3 is a longi'tdinalsectional ,view,

enlu-ged, of the several coinpressingst'ges;

5o Figs. 4, 5, 6, and/7 areisectionallviewsv taken respectively alongA the'linesAv 6- 6, 'and 7 -7 of Fig. 3, ofgthefsev al oo nl pressing stages. i [if 4,Similar reference characters A'indicate corend with anannular compression chambel 15 and lts Portwnvl water Jacketing 'spaces l Witl1 the Waterrv j ac ketin "pistoni rod. l2 5 is ,adapted jVhere rod pack y recessedfanged .end

stepped Water-.jacket cv linderjl'Oflla having.:

' bores of different.:v s diameters c onnected by-.an #annular beveled f .112 'constituting an .end `wall of thef sezonl` compression chamber, as will pore, 4 f1 1 11'y -1 appear; The ,outer c @Wall 13 s u rro1 11 `1 ds the oyllnders l0-11V in` 'annularl spacedjirelation landconstitutes a vis, admitted :the forsv hr present embodif comprises a; vtwo-` by "bolts withr ga@ redlicedr-diameterz n c linder portion'lO form-ingv theend -;v vall.of t e yfirst fr v'holes in the end wall 35 and the flange 44Y beveled connectin portlon the cylinder' portion v.p1stonend of the second stage compression Y piston projection 41 whose diameter is an exact fit wal1f35 provided with a central aperture 36.

Ihesteps of the pistons 33 and 34 correspond `lin .fdiameter with the bores of thecylinders `fin which they are fitted, and are rovided "with-suitable packing rings 37 an 38. A

39 between the to the inner surface of 12 and constitutes the Vpistons correspon chamber.

The piston rod passing into the rst .'s'tage compressing space from the cross-head is provided with a large flange 40 whose l.outside diameter and axial thickness is an :exact fit within the recessed end of the 33-34, and is provided with a reduced .Within the machined end of the third stage .tubular piston body 42. Bolts or studs 43 `are secured in the fiange and pass through "'ihoth stages being single acting.

The third stage piston body 42 is relai tively long and "extends axially in spaced relation within the hollow piston body 233-34 where it is engaged at its-end in the `third intermediate stage compression cylinder, 'the interior space of said piston 33-34 allowing the introduction vof the cylinder lbarrel 46 and water jacket'47 of said thi-rd l`compression stage.

V'Il-he third stage, cylinder and water jacketing .space 46-47 is provided witha wide `fiange 48 cast integrally therewith,` and at .lits marginal portion is machined, as at 49,

.to accurately fit the end of the cylinder 11, being secured thereto by bolts 50, this flange providing a means of correctly aligning the ithird stage cylinder bore with the `first and second stage cylinder bores, and also. acts asia .closing head for this end of the cylinder.

The fourth sta e compressing piston 51 is Aprovided with a s oulderd threaded stud 52 screwed into the outer or head fend 53 of the third compressing piston 42, and is heldin :absolute axial alignment with'the entire pis'- .tonassembly by ,'Ilhe 4,packing rings of the third stage Y.of `the built-up type consist of a num separate bull iston r of or spacing. ringsl 54 upon which are mounted regular piston rings 55,

this assembly being locked in position by 4.means of a flanged beveled collar 56 keyed `:upon `a `shouldered portion of the piston 51 properly machined surfaces."

and screwed up to a fixed position the outer end of the third stage .piston by means of the threaded stud 52. Y

The packing rings 58 of the fourth stage piston are ofvidentical type of construction to the third stage piston, and are held in place upon a threaded stud 59 by means of a piston nut 60.

Connecting to the third stage, and in absolute axial tandem alignment with it, is the fourth stage compression chamber, the fourth stage cylinder bushing '61 being secured at its ends within a cylindrical shell.

62 annularly spaced therefrom, 'said shell being provided with a flange 63 secured by bolts 64 to the end of the third stage cylinder, and having a reduced projecting end portion 65 beveled atits inner end in correspondence to fitted exactly into the recessed and machined end 66 of the third cylinder bore. .A cylinder-head 67 bolted to the flanged end 68 of the shell 62 closes the end of the fourth stage compression chamber.

A water reservoir 69 having a top-opening' 70, and surrounding the fourth stage in spaced relation, is secured to the third stage cylinder by bolts 71 and is in connection with the water jacketingspace' of the third stage through a passage 7.2, water being-admitted from the reservoir to the space between the fourth' stage cylinder bushing 61 and shell 62 through a passage 73. Water is admitted to the third stage waterl jacket through an intake pipe 74, finally passing into tie over-flow pipe 75 in the reservoir 69 and being returned to the tank 76 through a return pipe 77. f

The compression of the fluid in the third and fourth stages takes place as the pistons travel in a direction away from the power end of -the machine.

It will be seen from Athe above description that there are two sta es of compression, the first and second, of re ativel equal mechanical load value acting towar and two stages of compression, the third and fourth, also of relativelyequal values acting laway from ,the powerend, thus embodying the best conditions to equalize the stresses lon the crank shaftduring each revolution, resulting in a smoothly running compressor and one that is in the driving power required.

Eachof the compressing spaces is provided with the roper A'number of inlet and 4discharge va upon thesuction stroke and to be expelled upon the return stroke in the manner uSual in this type of apparatus.

The. inlet valves 78- for the first stage (Figs. 3 and '4) are provided in the su p y s the power end,

free from excessive variation ves to. permit ther fluid to'enter space 7 9 between the supply port 80 an the f' 'firststage compressing space, the discharge valves being between the compressing lao CII

` and the spaceand the discharge space 821y from which t, .e compressed/timid i conveyed-through@ conduit connectionS first; sta einter, cooler 84. `Yate isp-supplied; lto this linter` COQQI'TifEQnl .the ,Weten jacket-space of :the

8 5, and fis returned-tolthe tankltby means o f -anfoverfflQWL Pipe 85.*,vxflhei-intake port 80, byfnvvhich-E fluid enters from: thef external l space 8'( ,,formedHbetjyeengthe bfckf'fofa the hollowy differentialpiston )334-34 Land@ the Hanse-48,' et the: closing.; Ilenial commonly called the dead space?` l Vomeansoifpiping 88 and an inletopenin 8,9thisrpipe-lbeing slipported in a--fistandarQ01-which also 'acts as a'S'Il'PPOlb:012"' iallfay Qmpresor. 1f-'The ob-Vv j e'ct of this' co'n nect-ionl isrftwo-fold-frs'tfto IelYeI any :PFeSSllrethatfwOlllldresult from the 'movement otv the pistongyand second, .to

collect any leakage, past, the; pistons and 'return it to thefintak'e' port '80,. thus Preventing expensive` or* injurious as. v

.The inlet v alye the@ (Figs'. l3 and `5v) .isplaed'between ,thegwaterftrapped'inekeprwzianaalle ,space ,sa

by which tli'flidflefay esi'stetagevintel'- cooler 84 andtl'nise" u n s space the discharge v a 1ye, bctwee'r'il the,l compressing s pipeBZ conductsthe secondl fluid to maticalllyat98f`(pieferably in thetank 7 .Thewinlet valve99: for the the intake portlOQ'. stage inter-cooler Q8 third stageconipressing the latter 'beingcbn with the' th'ird'fst'zig coil submerged in'th The intake `Valver final stage' (Figs.3 a

tit)

third stage'y ht-Uleig 105 discharge Valve said'compressinfisp i' after-cooler, ,o 111 (1Preferably?" Letters "Patentv is A:

rstand secondcylindersybysmeans o'ffafpipe tcn artery; l ten'ing nuts 45-byrmeanscof asuitable wrench tage-en1p1essina 94 being placed.; ,Y ascend thefdijsf charge 'space'95. `and,discharge pmftgfi A Stageempres'sedfan inter-coler, indicated .diagram. @bil Subm@iran-f` tioirgealso, the lclearances.that fis', the distance betweenthe-jpiston and. head1 of thecylinder attheendof the; stroke,1:in this class of apparatus, ymust be' maintainedy 'at aff veryv` small figure, 's0 that itis desirable, in ,efe'cti ng -the quickzremoval and replacement' yof the pistons, ,topmaintain the exactoriginal kposition without* affectingY this small is .accomplished inthe present machine; inspectzgor remove the 'pistons it is but necessary yto Lremove thegbackstructu're by unbolting atthe flange 48, removing .the fas-'- to disconnect the ,kpistonnunitw assembly rfrom the pistonrodian e 40, and withdrawing the;l piston assemb y lfrom: cylinders 10 `-.Ans the; pist-onrod,`with"its flange 40, isk adjusted :oncev for all in the proper vrelationtothe frontjhead forV the clearancedesired,

the pistons ma f; be Iremoved and replaced an infinite num er.;of; times, Iwith thel assur-r ance ,that theyg;wi-ll;always. occupy .the fexact position neces'sa yxtowniaintain the small clearance desired inrv each case; Anfv important factor in lthe maintenance :of high effi# ciency, atall times, is'thereduction of gravitywearl on the -pistons land cylinders, due to the unit assembly of o the ,pistons and the method of support. The fourth stage piston 51 operates inthe remoyfable bushing 61, preferablygfof hardened steel, Aand-which acts asian outboard support, orfbear'ing, for that end of' the pistomassenlbly.. `The opposite j endthru the jpistonl rod 25, issupported by.

gear crosshead, thel downward Y the running wear andy pressure of lvthe intermediate and n conduits 11-71`and--118.

clearance. This .i

heavier pistons `beingrelieved,holding'v them Y perfectly central..in. their ,cylinders :and per- .ha've illustrated` atisfeizte'r'y embodiment. ofthe YI claim. ideslre'nto mitting the A piston ringsjto function prop. o

said, firs@ Sage:

piston having a skirt enterin the larger bore during the pistons stro e to form therewith an annularspace, a second stage piston connected to thev skirt of said first stage piston engaging the larger bore and acting'towards the step between said bores, the annular space between the larger diameter second stage cylinder and the skirt of said smaller diameter rst stage piston vconstituting the second stage compressing chamber.

2. In' a multi-stage compressor, a cylinder having a stepped bore, a cylinder-head closing the small end, a 4first stage piston engaging the smaller bore and acting towards said cylinder-head, and a second stage piston in integral continuation of vsaid first stage piston engaging the larger bore and acting towards the step between said bores, the annular space between the larger diameter second stage cylinderv and the smaller diameter firstrstage piston constituting the second stage compressing chamber.

3. In a multi-stage.compressor, a cylinder having a stepped bore, a cylinder-head closing the small end and having a piston rod bearing, a piston rod slidable in said bearing, a first stage piston connected to said piston rod engaging the smaller bore and acting towards said cylinder-head, said first stage piston having a skirt entering the larger bore duringv the pistons strokev to forni therewith an annular space, and a second stage piston connected to the skirt of said first stage piston engaging the larger bore and acting towards the step between said bores, the annular space between the larger diameter second stage cylinder and the skirt of said smaller diameter first stage piston constituting the second stage compressing chamber.

' 4. In amulti-stage compressor,

havin" a ste )ed bore a c linder-liead clos n l i ing -the small end, closure means for the larger end, a first stage piston engaging the smaller bore and acting towards the cylinder-head, said first stage piston having a skirt entering the larger bore during the pistons stroke to form therewith an annular space, a second'stage piston connected to the skirt of said first stage piston engaging the larger bore and acting towards the step between said bores, the annular space between pressing chamber,

a cylinderI Iskirt entering the larger bore during thev form therewith an annular stage piston connected `to v the skirt of said first stage piston engagingI the larger bore and acting towards the stepl between said bores, the annular space bepistons stroke to space, a second tween the skirt of said larger diameter. second stage cylinder meter first stage piston constitutingv the second stage compressing cliamber,tlie space between said pistons' and said closure means constituting a dead space, and fluid conf ducting means between said dead space and the first compressing stage.

6. In a multi-stage compressor, `a cylinder having a stepped bore, a cylinder-head closing the small end, a hollow stepped (piston member closed at its small end, inclu ingk a` small diameter first stage piston en aging the smaller bore and acting towar s said cylinder-head, and a large diameter second'l stage piston engaging the larger bore and acting towardsthe step between said bores, the. annular space between the larger diameter second stage cylinder and the smaller diameter first stage piston constituting the second stage compressing chamber.

7 Ina niulti-stage compressor, a cylinderr having a` stepped bore, a cylinder-head closing the small end and having a piston rod bearing, removable closure means for the large end, a piston rod slidable in said bear-l ing, a stepped piston member connected to sa'id piston rod at its small end, including a small diameter first stage piston engagingk the smaller bore and acting towards said cylinder-head, and 'a large diameter second stage piston engaging the larger bore and acting towards the. step between said bores, the annular space between the larger diameter second stage cylinder and the smaller diameter first stage piston constituting thek .second stage compressing chamber, said closure means adapted to be removed to permit removal of said piston member from thcV large diameterV end of said cylinder.

8. In a multi-stage compressor, a cylinder having a stepped bore. a cylinder-head closing the small end and having a piston rodi bearing, removable closure means for the:

large end, a piston rod slidable in said bear.-` ing, a stepped piston member, connection means between saidniember and the piston rod for removably connecting said piston to thev rod, said means being accessible -roni the large diameter end of said'cylinderfsaid;

piston member including a small diameterl rst stage piston engaging the smallerl bore and acting towards said cyclinder-head, and a. large diameter second stage piston engage bore and acting towards` theV ingthe larger step between said bores, the annular space;` between the larger and the smaller dia-- diameter second stage cylinder and the smaller diameter firststagey piston constituting the second stage coin-- 13@ and the smaller 'large end of the latter, said piston including a small d1-v ameter first stage piston engaging the smaller chamber. 'y

9. .In a multi-stage compressor, a cylinder having a stepped bore, a cylinder-head closlng t-he small end and having a piston rod bearing, removable closure means for the' large end, a piston rod slidable in said bearing, a hollow stepped piston, connection means between said piston rodand the small end of said piston accessible through the said piston for disconnectin bore and acting towards said cylinder-head, and a large diameter second stage piston engaging 'the larger bore and acting -towards the step between -said bores, the annular space 4 between the larger diameter second stage cylinder and the smaller diameter first I stage piston constituting the second stage compressing chamber, said closure means adapted `to be removed to permit removal of said piston member from the large diameterinder upon disconnection other .direction of recipr end of said cyl from said piston rod.

10. In a multi-stage compressor, a cylinder having a stepped bore, a vcylinder-head closing one end and Ahaving a piston rod bearing, closure means for the other end having a central bearing portlon, a stepped piston member, a. pistonrodslidable in said piston rod bearing and connected .to said piston, -an axial extension on said piston 1n :opposed direction to said lpiston-rod and slidably engaging said central bearing portion of the piston engaging the smaller bore and acting towards one end of the-cylinder, anda large diameter second stage piston engaglng the larger bore and acting towards the step between said bores, the larger diameter second stage cylinder diameter first stage piston constituting th second stage compressing 11. In a multi-stage compressor, a plurality of co-axial cylinders including afirstand second stage cylinder, a reciprocating piston assembly including first and second stage pistonsoperatin to compress fini in the same direction of reciprocation, a third stage co-a'xial cylinder. extension carried by stage cylinder to compress fiuid in the other direction of reciprocation.v

1 2. In'a multi-stage* compressor, a cylinder having a stepped bore, including first and second stage cylinder portions, a" cylinder-head closing the small end, a first stage piston engaging the smaller bore and acting 'towards said! cylinder-head, saidfirst stage to permit removal lof. said l closure means, said piston memvber including. a small diameter first stage the annular space between in said respective. cylinders said lengaging said third bore during theA pistons stroke to piston having a skirt entering the larger bore during the pistonsstroke to form therewith an annular space, a second stage piston con- -nected to the skirtof said first stage piston 'gaging'said third stage cylinder to com ress fiuid in the direction opposed to the irection of compression in the first and second stages.A

13. In a multi-stage compressor, a plurality of co-axial cylinders including a first and second stage cylinder, a reciprocating piston assembly including first and second stage 'pistons operating in said respective cyllnders to compress fluid in the same direction of reciprocation, a third stage cofaxial.

cylinder, and an; axial pistonjextension carried by said piston assemblyengaging said third stage cylinder to com ress fiuid in the ation, said first e.v pistons/ and said third ing s aced to provide a said rst and second stage and second st stage cylinder dead space behind pistons.

'14..In a multi-stage-compressor, a cylinder having a stepped bore including first and second stage cyli der-head closing the means for the large end small end` closure provided with a central third stage cylinder portion, a first stage piston engaging the smaller bore and acting towards the cylinder-head, said first stage piston having a skirt entering the larger bore during the pistons stroke to -form therewith Aan vannular space, a second stage piston vconnected to the skirt of said first .stage piston engaging the larger bore and acting towards the step between said bores, the' annular space between the skirt of said larger diameter second stage cylinder andthe smaller diameter first stage piston constituting the' second stage compressing chamber, anda third stage axial piston ex- "tension connection to said first and second stage pistons engaging said third stage cylinder to compress fluid in the direction opposed to the direction ofcompression in first and second stages.

15. Ina multiis'tage compressor, a cylin der having. a stepped bore including .first and. second stage lc vlinder portions, a cylinder-head closing `the small end, a hollow stepped piston assembly closed lat its small end,- including asmall diameter firstv stage piston engagingthe Vsmaller bore and acting towards said cylinder-head, said first stage piston having a skirt entering the lzrger orm stage piston constituting vthe der portions, a cylintherewith an annular space, andv a larger diameter second stage piston engaging the larger bore and acting towards the step betweensaid bores. the annular space between the skirt of said larger diameter second stage cylinder and the smaller diameter first stage piston constituting the second stage compressing chamber, a third stage cylinder co-axial with said first and second stage cylinders and projecting into the hollow of said first and second stage piston assembly, and a third stage axial piston extension carried by said piston assembly engaging said third stage cylinder to compress fluid in the direction opposed to the direction of compression in said first and second stages.

16. Ina multi-stage compressor, a cylinder having a stepped borev1 including first and second stage cylinder portions, a cylinder-head closing the small end and having a piston rod bearing, removable closure means for the large end, including Aa central third stage c linder portion, a piston rod slidable iny sai bearing, a stepped piston member connected to said piston rod at its small end, including a small diameter first stage piston engaging the smaller bore and acting towards said cylinder-head, and a large diameter second stage piston engaging the larger, bore and acting towards the step between said bores, the annular 'space between the larger diameter second stage cylinder and the smaller diameter first stage piston constituting the second stage compressing chamber, a third stage axial piston extension carried by'said piston memberengaging said third stage cylinder to compress fiuid in the direction opposed to the direction of compression in the first and-second stages, said closure means adapted to be axially removed to .permit removal fofsaid piston member from the larger diameter end ofV said stepped cylinder.

17. In a multi-stage compressor, a cylinder having a stepped bore, including first and second stage cylinder portions, a cylinder-head closing the small end and having a piston rod bearing, removable closure means for the large end, including an inwardly-extending third stage cylinder portion in annular spacedr relation to said stepped cylider, a piston rod slidable in said bearing, a hollow stepped piston, connection means between said piston rod and the small end of said piston accessible through the large end of said piston for. disconnecting the latter, said piston including a small diameter first stagel piston engaging the smaller bore and acting towards said cylinder-head, .and a large diameter second stage.

piston engaging the larger boreand acting towardsjthe step between said bores, the annular space between the larger diameter second stage cylinder and the smaller diameter` first stage piston constituting the second and second stage cylinders,

weaves stage compressing chamber, and a third stage axial piston extension carried by said piston member engaging said third stage cylinder to compress fiuid in the direction opposed to the direction of compression of the first and second stages, said closure means adapted to be removed to permit removal of said piston member from the large diameter end of saidy cylinder upon disconnection from said piston rod.

18. In a multi-Stagecompressor, a plurality' of coaxial cylinders, including a first and second stage cylinder, a reciprocating piston assembly, including first and second stage pistons operating in said respective cylinders to compress fluid in the same direction of reciprocation, third and fourth stage co-axial cylinders, and an axial piston extension carried by said piston assembly including third and fourth stage pistons ento compress fluid in the other direction of reciprocation.

19. In a multi-stage compressor, a stepped cylinder including first and second stage cyl- -inder portions, a reciprocating piston assembly, including first and secon stage stepped pistons operating in saidrespective cylinder portions to compress fluid 1n the same direction of reciprocation, a stepped cylinder including third and fourth stage cylinder portions in co-axial alignment with said first and an axial stepped piston extension carried by said piston assembly, including third and fourth stage pistons engaging said third and fourth stage cylinders to compress fluid in the other direction of reciprocation.

20. In a multi-stage compressor, aplural- 05 ityk of coaxial cylinders, including a first and second stage cylinder, a reciprocating piston assembly, including first and second stage pist-ons operating in said respective cylinders to compress fluid rin the same direction of reciprocation, third and fourth stage coaxial cylinders, andan axial'piston extension carried by said piston assembly, including third and fourth stage pistons engaging the third and fourth'stage cylinders to compress Huid in the other direction of reciprocation, said third` stage cylinder being spaced with, relation to said first and secondl stage pistonsto provide a dead space behind said first and second stage pistons.

21. In a multi-stage compressor, a plurality of co-axial cylinders, including a first and second stage cylinder, a reciprocating piston assembly, including first and second stage pistons operating `said respective cylinders to compress fluid in the same directionof reciprocation, third and fourth stage co-axial stepped cylinders, and an axial piston extension carried by said piston assembly, including a large diameter third stage piston secured at one end to said pisf 1,628,7es

ton assembly, and a smaller diameter fourth stage piston extending from said third stage piston, said third and 'fourth stage pistons engaging said third and fourth stage cylinders to compress fluid in the other direction of reciprocation, the annular space between said large diameter third stage cylinder and the smaller diameter fourth stage piston constituting the third stage compressing chamber.

22. In a multi-Stage compressor, a plurality lofco-axial cylinders, including a first and second stage cylinder, a reciprocating piston assembly, including first and second stage pistons operating in said respective cyhnders to compress fluid in the same direction of reciprocation, third and fourth stage co-axial stepped cylinders, including ay large diameter third stage pistonV secured at one end to said piston assembly, and a smaller diameter-fourth stage piston removably secured to andv extending from Said third stage piston, said third' and fourth.

vstage pistons engaging said third and fourth stage cylinders to compress fluid in the other.

direction of reciprocation, the annular space between said large diameter third stage cylinder and the smaller diameter fourth Stage pistonconstituting the third stagecompressing chamber. Signed at Bridgeport, in the county of Fairfield and State of day of June A. D. 1926. v ALEXANDER' W. LIMON T, J R.

Connecticut, this 24th 

